This invention relates to novel organic dyes which are active in the photochemical disinfection of effluents. Sewage effluents of domestic, agricultural or other origins contain large amounts of microbiological pollutants which are not destroyed by treatment in activated sludge plants. Therefore, water resulting from such treatment is unsuitable for human consumption or agricultural use and, after penetrating into ground water, gives rise to health and epidemiological hazards.
A photochemical procedure for disinfection of effluents consists of their treatment with small amounts of certain dyes in the presence of oxygen dissolved in the effluent and visible light (sun or artificial light). The dye absorbs the light energy and transfers it to the oxygen molecules which are then capable of destroying the microorganisms. Alternatively, the dye, after absorbing light energy, acts directly upon the microorganism leading to their annihilation.
The use of methylene blue as a dye in the photochemical disinfection of effluents is known. Thus, domestic sewage effluents which had been previously treated in activated sludge plants, have been disinfected by dissolving therein minute amounts (say 2 ppm) of methylene blue and subjecting the solution to visible light irradiation in the presence of air. However, the use of methylene blue in such disinfection processes is not fully satisfactory because of the tendency of this dye to be adsorbed by clays and soil components which are present in the aqueous effluent. This tendency can be ascribed perhaps to the high degree of dissociation of methylene blue. Another drawback of the use of methylene blue in the aforementioned process is its instability towards active oxygen species which are generated in the treated water in the course of the photochemical process.